This invention relates to quantity gauging.
The invention relates to systems and methods of quantity gauging and, more particularly, but not exclusively, to fuel-gauging systems and methods.
Conventional fuel-gauging systems may employ a capacitive sensor consisting of a tubular outer electrode and a concentric inner electrode. The sensor is mounted on the floor of the fuel tank projecting upwardly, the outer electrode being filled with fuel to the same level as in the tank. The capacitance between the two electrodes changes as fuel level changes and, by measuring the capacitance, an indication of fuel height can be obtained. Alternatively, the system may employ an ultrasonic sensor in which an ultrasonic transducer is mounted on the floor of the tank. The transducer transmits ultrasonic pulses upwardly through the fuel to its interface with gas above the fuel where the pulses are reflected. By measuring the time taken between transmitting a pulse and receiving its reflection, the height of fuel can be calculated. This is sometimes referred to as a xe2x80x9cbottom-upxe2x80x9d technique. Usually, ultrasonic gauges of this kind employ a still well, that is, a tube in which the acoustic pulses are confined. Ultrasonic gauges are also used in a xe2x80x9ctop-downxe2x80x9d technique where the transducer is mounted above the level of the substance being measured and the pulses are transmitted down through air to the surface of the substance, where they are reflected back to the transducer. Examples of ultrasonic gauging systems are described in GB2311373, GB2290141, GB2270160, GB2265005, GB2265219 and GB2340603.
There are various difficulties associated with ultrasonic or acoustic level measurement. Measurements may become inaccurate when the surface of the liquid is disturbed in some way, such as by the presence of foam, waves or by being at an angle. It is important to be able to determine whether or not a measurement of height from a sensor is accurate and whether the sensor is functioning correctly.
It is an object of the present invention to provide an alternative quantity gauging system, probe and method.
According to one aspect of the present invention there is provided a quantity-gauging system including first means for determining the distance below a first location of an interface between two different fluids and second means for determining the distance of the interface above a second location, the outputs of the first and second means being supplied to means for determining an indication of quantity of one of the fluids.
One or both of the first and second means preferably include acoustic means for generating pulses of acoustic energy towards the interface. The system may include a still well having the first and second means mounted at opposite ends of the still well. The second means may include capacitive electrodes. Alternatively, the second means may include acoustic means for generating a pulse of acoustic energy up towards the interface, the first means including capacitive electrodes. One of the first and second means may include a pair of concentric tubular capacitive electrodes, the other of the first and second means including acoustic means arranged to direct a pulse of acoustic energy along the centre of the inner electrode. The first and second means may include acoustic means for generating pulses of acoustic energy towards the interface from opposite sides, the system additionally including capacitive electrodes for providing an additional indication of the position of the interface. The capacitive electrodes are preferably a pair of concentric tubular electrodes, the acoustic means being arranged to direct pulses of acoustic energy along the centre of the inner electrode. One fluid is preferably a liquid and the other fluid is a gas above the liquid.
According to a second aspect of the present invention there is provided a quantity-gauging system including means located in a fluid for providing an indication of the height of the fluid above a lower location, means located above the fluid for providing an indication of the distance of the fluid surface below an upper location and means for comparing the outputs of the first and second means to determine if the system is performing accurately.
The system may include a plurality of probes, each probe including first and second means.
According to a third aspect of the present invention there is provided a quantity-gauging probe including first and second means for providing separate indications of the height of fluid along the probe.
According to a fourth aspect of the present invention there is provided a method of determining an indication of the quantity of a fluid including the steps of determining the height of an interface of the fluid above a first location below the interface, determining the distance of the interface below a second location above the interface, and determining the quantity of fluid accordingly.
An aircraft fuel-gauging system and method according to the present invention will now be described, by way of example, with reference to the accompanying drawings.